1. Field of the Invention
The present invention relates to recording/playback apparatuses for recording or playing back optical recording media, such as recording optical discs, and also relates to laser drive pulse adjusting methods. In particular, the invention relates to a technique for suitably performing laser drive pulse adjustments in consideration of a case where the optimum recording power is changed due to various conditions.
2. Description of the Related Art
In optical-disc recording technologies, a recording parameter representing, for example, a recording waveform formed by a laser, is referred to as a “write strategy”, and a laser is emitted on the basis of this write strategy so that information can be recorded. When recording information on optical discs, the recording parameter forming the write strategy is adjusted to implement the high recording quality. This is referred to as “write strategy adjustments”.
The write strategy adjustments are performed by making correction to a reference strategy. The reference strategy is a basic strategy, which is a predetermined reference. A specific numerical value of the reference strategy can be set by a media manufacturer (prestored in a medium) or is prestored in a drive.
Generally, the write strategy adjustments can be performed for each optical disc to be loaded in a drive. That is, the write strategy is closely related to the material and thickness of the recording film of an optical disc, the configuration of the grooves, the recording speed, etc. It is thus necessary that the write strategy be optimized for each optical disc.
Write strategy adjustments are also necessary for absorbing variations in drives.
In this case, it is necessary that a drive perform write strategy adjustments. The reasons for this are as follows.
In the market, many types of optical discs that are difficult to be handled by drive manufacturers are distributed, and to set suitable write strategies for all optical discs distributed in the market, numerous steps are necessary. This is time-consuming and also raises the cost of drives. Additionally, handling media that are distributed after drives are shipped requires updating of the firmware of the drives, which is also time-consuming.
Because of the above-described reasons, it is demanded that write strategy adjustments be performed by a drive when performing recording.
In recording optical discs, before recording actual data, calibration is generally performed by means of test recording so that optimum recording power can be calculated. Such a calibration operation is referred to as “optimum power control” (OPC).
By performing OPC, even if an objective lens is stained, for example, the optimum recording power can be reset, and the recording quality can be effectively maintained.
However, even if the recording power is optimized by performing OPC, there is a possibility that the optimized recording power be changed due to various factors, such as variations in the recording sensitivity on the disc surface, a change in the temperature of a pickup, variations in the thickness of the substrate of the optical disc, and stain on the optical disc. As a result, the recording power set by performing OPC may deviate from the optimum point.
From this point of view, it is necessary to adjust the write strategy such that relatively high recording characteristics can be maintained even if the recording power deviates from the optimum point. That is, it is necessary that the recording power margin is wide.
To ensure a wide recording power margin, write strategy adjustments are hitherto performed by the following approaches.
One approach is to manually perform write strategy adjustments. First of all, recording/playback is performed by the use of a certain level of recording power, and then, a write strategy that can improve the quality of a recording signal with this recording power is searched. Then, it is checked whether the recording power margin is increased with the searched write strategy. If the recording power margin is not increased, another write strategy is searched. Such an operation is repeated through trial-and-error operations.
Another approach is as follows. Write strategy adjustments are performed with a certain level of recording power (e.g., the recording power optimized by performing OPC) by the use of a reference strategy as an initial value so that the quality of a recording signal with this recording power is improved. That is, the write strategy is adjusted to a strategy that can maximize the quality of a recording signal with a certain level of recording power, and it is assumed that the quality of a recording signal is also improved with another level of recording power.
Patent Numbers 3766994 and 3632849 and Japanese Unexamined Patent Application Publication No. 2000-182244 are examples of the above-described related art.